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A Guide to Adjusting Your Hot Water Heater Temperature Setting
This guide explains how to adjust the water heater temperature setting on your A. O. Smith water heater and describes the different control systems for electric and gas water heaters.
Table of Contents
It also includes sections on choosing the best hot water temperatures for your home and the benefits of reducing the hot water temperature. This guide also covers solutions to common hot water tank problems. While this guide provides detailed instructions for adjusting your hot water temperature, it's best to contact an approved A. O. Smith plumbing professional if you're not comfortable performing these steps.
What Temperature Should a Water Heater Be Set At?
The best temperature for a water heater is one that provides sufficient hot water for your applications and is neither too hot nor too cold. It’s best to avoid excessively high water temperatures, as they increase the risk of scalding, particularly for children. On the other hand, water temperatures that are too low may not provide sufficient hot water and may encourage the growth of harmful bacteria.
Higher hot water temperatures can be helpful if you have a dishwasher and clothes washer that doesn't have a supplementary water heater. Living in a larger home where the distance from the hot water tank to the point of usage results in an excessive water temperature drop can also be a reason to turn up the thermostat. If you prefer higher water temperatures, it's best to install thermostatic mixing to regulate the water temperature at each faucet.
How to Adjust Your Water Heater’s Temperature
The steps to adjust your water heater temperature differ depending on the type of water heater installed and whether the water heater has an electronic controller.
How to Adjust Temperature on an Electric Water Heater With a Standard Thermostat
This instruction applies to electric tank water heaters that have one or two thermostats. To verify the type of water heater, consult your manual. Adjusting these types of thermostats entails switching off the power and opening the element access panels. Electricity is dangerous, and there’s a risk of electric shock. Unless you have proper knowledge, it’s safer to contact an electrician or A. O. Smith Service provider.
Step 1: Turn off the Power at the Circuit Breaker
Disconnect the power supply to the water heater by switching off the circuit breakers in the electrical service panel. As most heaters have two elements, you must adjust both thermostats. To check you’ve isolated the electrical supply correctly, remove the cover for the electrical junction box on the water heater and use a circuit tester to check there’s no power. The junction box is usually located on top of the water heater.
Step 2: Unscrew the Access Panels and Gently Adjust The Insulation
Locate the element access panel. There’s often a top and bottom panel, each containing a heating element. Remove the panel covers using a Phillips screwdriver. Gently adjust the insulation out of the way so you can access the thermostats. Some water heaters have two thermostats — one in each access panel — and others have only one that is located in the bottom panel.
Step 3: Adjust the Water Heater’s Thermostat
Using a flat-blade screwdriver, adjust the thermostat to the desired temperature setting. Turn clockwise to increase the temperature and counterclockwise to reduce it. Thermostats of most domestic electric water heaters have a temperature range from 95 degrees Fahrenheit up to 150 degrees Fahrenheit. If there are two thermostats, set them to the same temperature.
Water heaters set to high temperatures pose a significant burn risk, and may result in a hot water-related injury. Touching water above 120°F (49°C) may result in hot water-related injuries, as temperatures above this level can cause severe burns within seconds. At 140°F (60°C), it takes just a second for a serious burn to occur. To reduce this risk, it's recommended to set the water heater thermostat to no higher than 120°F. Regular maintenance of water heaters is essential to ensure they are functioning correctly, and safety measures like anti-scald devices and temperature limiters can further protect vulnerable individuals.
| Temperature | Time to Produce a Serious Burn |
|---|---|
| 120˚F (40˚C) | More than 5 minutes |
| 125˚F (52˚C) | 1½ to 2 minutes |
| 130˚F (54˚C) | About 30 seconds |
| 135˚F (57˚C) | About 10 seconds |
| 140˚F (60˚C) | Less than 5 seconds |
| 145˚F (63˚C) | Less than 3 seconds |
| 150˚F (66˚C) | About 1½ seconds |
| 155˚F (68˚C) | About 1 second |
Step 4: Replace the Insulation, Seal Everything and Restart the Water Heater
Push the insulation back into place and replace the heating element covers. Ensure the terminal box cover is secured before you turn the power on at the circuit breakers. Allow the heater time to settle, and check the water temperature by running the faucet.
Gas Water Heaters
The thermostat for standard gas water heaters is part of the gas control valve fitted at the bottom of the water heater. Turn the knob to the desired temperature. If there are several settings and you're not sure what the temperature range for each is, consult the manual.
If the gas heater is off, follow the instructions in the manual or on the gas control valve for lighting the heater. VAC mode is a vacation setting that controls the water temperature at 55 degrees Fahrenheit when you're away.
Water Heaters With Electronic Controls
Certain tank water heaters have an electronic controller. Electric water heaters have a control assembly, and gas water heaters have a user interface module (UIM). Using these controllers, you can adjust the hot water heater temperature setting to any temperature between 95 degrees Fahrenheit and 150 degrees Fahrenheit.
Hot Water Heater Settings
The temperature range of A. O. Smith hot water heaters lets you set the water temperature to suit your unique requirements. Understanding what the lowest and highest safe temperatures are can help you choose what's right for your home.
Lowest Safe Temperature
The primary concern about low hot water temperatures is the possibility that harmful waterborne bacteria can grow. The CDC lists several potentially harmful bacteria that can grow in the home’s water system. For this reason, the recommended minimum hot water temperature is 120 degrees Fahrenheit, as this is sufficient to kill most bacteria.
Highest Safe Temperature
Hotter water kills more bacteria, and this may be a consideration for people at risk of waterborne diseases, such as the elderly, those with weakened immune systems or certain diseases and infants. But at the same time, the hotter the water, the greater the risk of scalding. The approximate time for adults to suffer second- or third-degree burns from exposure to hot water is as follows:
- 120 degrees Fahrenheit: More than 5 minutes
- 125 degrees Fahrenheit: Approximately 2 minutes
- 130 degrees Fahrenheit: Around 30 seconds
- 140 degrees Fahrenheit: Less than 5 seconds
- 150 degrees Fahrenheit: Within a few seconds
(*Do not test these approximations yourself.)
Average Safe Operating Temperature for the Average Consumer
The safest water heater temperature setting is between 120 degrees Fahrenheit and 140 degrees Fahrenheit. All A. O. Smith hot water heaters come preset for 120 degrees Fahrenheit, and this temperature should suit most consumers.
Thermostatic Mixing Valves
Thermostatic mixing valves can control hot water temperature at faucets and eliminate the risk of scalding. Fitted with a hot and cold water pipe, thermostatic mixing valves automatically control the maximum water temperature. You can adjust the temperature to suit your personal preferences. An added advantage is that the water temperature remains constant, and these valves can increase the amount of usable hot water.
Solutions to Common Hot Water Tank Problems
Although your A. O. Smith water heater will give many years of good service, you may occasionally experience problems with the hot water supply. Here are some common problems that may occur and how to diagnose them. If you’re handy, you may be able to fix them, but in other instances, it’s best to get help from a plumbing contractor.
No Hot Water
There’s nothing worse than a cold shower when your water heater fails to come on. Sometimes, the cause is quite simple, so it’s best to perform a few checks before calling a plumber. For a gas water heater, check that the pilot light is lit by verifying that the status light on the gas control valve is flashing once every 3 seconds. If the light is off, try to relight the pilot light following the instructions in the manual or on the water tank. Alternatively, if the status light flashes more than once every 3 seconds, you may need to contact a plumbing contractor.
For electric water heaters, check and reset the circuit breaker. If this doesn’t work, contact a plumbing contractor.
Inadequate Hot Water
If the water isn’t hot enough or seems to run out too quickly, adjust the thermostat to a higher temperature. If the problem persists, contact a plumbing contractor.
Strange Noises
If you hear a popping or rumbling noise coming from the water heater, it may be caused by the accumulation of sediment or aluminum hydroxide. Sediment collects at the bottom of the water heater, trapping boiling water. Another possibility is the accumulation of scale on the heating elements. Try flushing the water heater to see if this resolves the problem. If you live in a hard water area, flush your water heater more often. Alternatively, if the problem persists, consider installing a water softener on the water supply line to minimize sediment accumulation.
Leaking Tank
You may have a leak if you notice water in the drain pan or on the floor near the unit. Common reasons for water leaks include loose piping connections, a faulty drain valve, or a faulty water tank. Address leaks immediately to reduce the risk of water damage from a burst pipe, fitting or tank. Check all fittings for leaks and tighten them if necessary. If water appears to be coming from the tank, it may be corroded and need to be replaced. If you can’t identify or fix the leak, contact a plumbing contractor.
Rusty or Discolored Water
Brown discolored water running out of the hot water faucet is a sign of non-harmful bacteria in the water tank. Another sign is that the water may have a sulfur-like smell. Contact a plumbing contractor. or your nearest A. O. Smith supplier and consider flushing the water heater tank more frequently.
High Energy Bills
According to the Department of Energy, the water heater is the second largest energy user in the home, typically accounting for around 18% percent of your energy consumption. You can reduce energy bills by setting the thermostat to an optimal temperature of 120 degrees Fahrenheit. Also, consider insulating hot water pipes to reduce heat loss. If your water heater is old, consider upgrading to a more energy-efficient water heater such as a hybrid electric heat pump system, condensing gas water heater or tankless system.
Water Heater Keeps Turning Off
If your electric water heater keeps turning off, it may have a faulty thermostat or a defective heating element. You can check using an electrical tester, but it's safer to contact a plumbing contractor if you don't feel comfortable doing this. If the water heater has an electronic controller, it may display a fault code. If you have a gas water heater, check the status light on the gas control valve. If it’s flashing more than once every 3 seconds, refer to the water heater manual. Possible reasons for intermittent operation include an electrical fault, blocked air filter or faulty ventilation system. For safety reasons, do not try to dismantle any components on the gas water heater; always contact a plumbing contractor for assistance.
What Are the Benefits of Lowering My Water Heater Temperature?
While it’s great to have a long, hot shower, reducing the temperature of your hot water heater to a recommended level has significant benefits. These include a lower risk of scalding, less sediment buildup, and reduced energy costs.
Reduces the Risk of Scalding
Hot water is dangerous. Water that’s heated above 120 degrees Fahrenheit can scald quickly. The hotter the water, the more quickly it can scald your skin. Even inadvertently putting your hand under a hot water faucet or stepping into a hot bath can cause burns. The recommended hot water temperature is 120 degrees Fahrenheit for most people.
Reduce Sediment Buildup
If you set the thermostat at 120 degrees Fahrenheit, you’ll reduce sediment buildup. Sediment interferes with the water heater's efficiency, and excess buildup can cause hot spots, leading to shorter water heater life. Even if the water is not that hard, you’ll notice a difference in the amount and rate of sediment building up.
Saves Energy
The energy needed to heat water to 140 degrees Fahrenheit is significantly higher than what is required to heat it to 120 degrees. Assuming your cold water is at 60 degrees Fahrenheit, you’ll use nearly 25% less energy to heat the water to 120 degrees Fahrenheit than to 140 degrees Fahrenheit.
Want to Upgrade Your Water Heater?
An efficient and reliable water heater is an essential component of modern life that you can’t do without. Water heaters can typically last for 10 or more years, especially those with modern glass linings. However, a leak in the tank of a water heater cannot be repaired, and it must be replaced. Older water heaters aren’t as energy efficient as newer models, leading to higher energy bills. If your water heater can’t keep up with your family’s needs, it may be time to check out our water heater selector quiz and contact a plumbing contractor for assistance about a new water heater.
Problems With Your Water Heater?
Have you had the water heater serviced recently? Are you experiencing problems such as poor heating, peculiar noises or dirty hot water? Your water heater should be flushed annually, and if it’s a gas water heater, it requires periodic inspection and servicing. Professionals best perform these maintenance tasks and we recommend contacting a plumbing contractor for assistance.
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Why A. O. Smith?
A. O. Smith is a leading manufacturer of both residential and commercial water heating technologies, including the #1 most specified commercial water heater.
For more than 145 years, we’ve developed state-of-the art products that push new boundaries and improve the lives of our customers.
We combine cutting-edge technology with committed people who take pride in providing the very best support for our customers.
Our products are put through rigorous quality and endurance testing so now matter where hot water is needed, A. O. Smith can provide a solution you can count on.